COMPLETE BLOOD COUNT (CBC)
The CBC quantifies the types of cells in a blood sample---specifically the red cells, the white cells and the platelets. Run on a sample of whole blood that has been blended with an anticoagulant, the CBC is a generalpurpose screening tool that can yield a great deal of information about a horse’s general health. “Results of the CBC can help determine a variety of physiological responses,” says Peggy Marsh, DVM, DACVIM, DACVECC, of Equine Medical Associates in Lexington, Kentucky.
The results of a CBC are broken out into several different components. For example, a test may describe the total number of red blood cells (RBC count) as well as hemoglobin, the total amount of oxygen-carrying protein in the blood. Another indicator is the hematocrit, also called the packed cell volume (PCV), which is the percentage of the whole blood that consists of red cells. More specific tests, such as mean corpuscular volume (MCV), might look at the average sizes and composition of the red blood cells.
Low red cell and hematocrit values might indicate anemia; high values might point toward dehydration. But this information is only a starting point. “The red blood cell information can sometimes help us focus on specific diseases, but is not very definitive,” says Katherine Wilson, DVM, DACVIM, of the Virginia–Maryland Regional College of Veterinary Medicine.
In fact, she adds, “RBC count is probably the least helpful information because horses usually don’t have big changes in red blood cell numbers. It is not uncommon for horses to have an RBC count a little lower than normal range, however. The term we use for low RBC is anemia, but unless the count gets very low, a horse doesn’t necessarily need to be treated for that condition. A lot of diseases or any chronic long-term disease can cause mild anemia. Usually if we see mild anemia on the bloodwork and the horse has other issues, the anemia is just an indication that we need to fix/treat another problem.”
Blood analysis also focuses on the white blood cell count (WBC count), a measure of the number of the infection-fighting white blood cells in the sample. This test may also be broken down into a white blood cell differential, which is a count of the numbers of each of the five specific types of white cells: neutrophils, lymphocytes, monocytes, eosinophils and basophils.
An elevated WBC count usually indicates infection or inflammation, and a closer look at the specific types of cells can yield clues to the type of process at work. “Usually if there is some kind of infectious disease, one or two types of white blood cells may be elevated,”